The atmosphere of air containing salt in saltwater coastal communities is particularly conducive to promoting and accelerating corrosion of exposed steel used in the piping of fire sprinkler systems, as well as various elements used in fire sprinkler heads during manufacture. The atmosphere creates a specific corrosion problem for exposed steel fire sprinkler systems.
National Fire Protection Association #13, Standard For The Installation of Sprinkler Systems, states, “Where corrosive conditions exist or piping is exposed to weather, corrosion-resistant types of pipe, fittings, and hangers or protective corrosion-resistant coatings shall be used.”
Typical fire sprinkler installations, such as ones that exist in outdoor parking garages in coastal communities, are extremely subject to corrosion. In order to meet the N.F.P.A #13 requirements as stated in the above paragraph [0002], standard industry practice is the use of hot-dipped galvanized pipe, fittings, and hangers in installation of fire sprinkler systems exposed to corrosion. Hanger rod is typically zinc plated all-thread rod. Occasionally, the hanger rings supporting the pipe are stainless steel, but usually they are simply galvanized. Fire sprinkler heads are usually painted polyester or Teflon coated for corrosion resistance by the manufacturer. But, severe corrosion occurs anyway, mostly due to fabrication techniques as described below, and the corrosion resistance fails in application.
Fire sprinkler systems are typically pre-fabricated. The sprinkler system is defined as a combination of “mains” and “branch lines”, similar to a tree where the trunk is the “main” and the branches are “branch lines”.
Fabrication of fire sprinkler mains involves the use of full lengths of sprinkler mainpipe (21 ft, or 25 ft.) and attaching outlets to the pipe for branch lines. The size of pipe used in sprinkler mains ranges from 2-inch through 8-inch, sized hydraulically using calculations. The outlets are made by cutting a hole in the pipe, and the use of hot-dipped galvanized outlets (threaded or grooved), welded to the pipe. Fabricated branch lines are either full lengths of pipe with welded outlets as described above for the sprinkler heads, or cut to length threaded branch lines with hot-dipped threaded galvanized fittings for the sprinkler head outlets.
The action of welding the outlets to pipe—either main or branch line, burns away the galvanization of the pipe and outlet. The action of threading the branch line pipe for screwed on galvanized fittings cuts away the galvanic layer of the pipe. In both instances with galvanization removed, the pipe or welded outlet becomes unprotected black steel, and extremely vulnerable to corrosion. The connections become the weak areas in the tire sprinkler systems, making them subject to failure which could be catastrophic. The repair of corroded pipe and outlets usually results in replacement of the entire section (full length) of pipe.
Stainless steel hanger rings furnish superior corrosion resistance, but when attached to the hot-dipped galvanized sprinkler piping, electrolysis (galvanic corrosion takes place as stainless steel rings and hot dipped galvanized steel pipe are dissimilar materials. The resulting corrosion takes place on the piping making it subject to failure. Also, typical zinc plated hanger rods corrode and can no longer support the weight of water filled pipe.
The industry standard of using polyester coated, or Teflon coated fire sprinklers meets the criteria of being corrosion-resistant, but corrosion occurs anyway, making the fire sprinkler heads subject to failure.